The reaction catalyzed by glutamate dehydrogenase holds a central position in metabolism. Glutamate, alphaketoglutartae and NH4+ are all important metabolites. In addition GDH utilizes either NAD+(H) or NADP+(H) as coenzyme. As such GDH appears to be an important site of regulation. GDH is an oligomeric enzyme exhibiting both homotropic andheterotropic interactions. Equilibrium binding studies and initial rate kinetics show negative cooperativity with respect to the coenzyme. In addition, a complex series f regulators modify the behaviour of the enxzyme, including ADP, GRP and leucine. The objectives of the research are two fold: 1) to elucidate the mechanism of, and hence infer a function for, the negative homotropic interactions. 2) to obtain a fuller understanding of how a variety of potential in vivo regulatory molecules such as ADP, GTP, and leucine exert their affects or how interplay between these regulatory molecules may control GDH. To achieve these objective, three phases of the glutamate dehydrogenase reaction will be studied in detail; substrate addition, product release and the chemical interconversion steps. Data will be accumulated using initial rate kinetics, equilibrium binding studies, and stopped flow kinetics on native glutamate dehydrogenase and several forms of the enzyme produced by chemical modification. Emphasis will be placed on a correlation of these studies and the effects of addition of ADP, GTP or leucine, either alone or in various combinations will examined. The effects of pH will be studied in detail. In addition, the ability of the enzyme to utilize NAD(H) and NADP(H) will be examined using coenzyme analogs, and the effects of varius regulators on these reactions will be examined to ascertain whether or not regulator molecules can affect the relative utilization of these coenzymes. To assist in correlating in vitro results with in vivo situations we shall mimic in vivo concentration ranges of substrates and regulators where possible, and perform some studies with intact mitochondria to try to establish in vivo significance.